I have G. sp "Rio caroni", my mix is 2m3f (I think). The fish scuffle with each other a lot, but no damage ever occurs. You for sure need more than a pair. I'm actually growing out 7 of my groups fry to add back into the group to see how they act in a larger group. Guianacara are my absolute favorite genus.
You can try separating and reintroducing until they breed. Then you can grow out a group.I wish I had owroewefi, they have beautiful yellow when spawning.

